1. Field of the Invention
The present invention relates to a sensing apparatus and movable body-mountable electronic equipment utilizing such an apparatus, and particularly to a sensing apparatus for detecting a physical quantity having a direction, such as acceleration and the electronic equipment, which utilizes such a sensing apparatus and is to be mounted on a movable body such as a vehicle.
2. Description of the Related Art
There has recently been widely available an apparatus for detecting the current position of a vehicle to facilitate movement of the vehicle, i.e., a so-called navigation apparatus.
The conventional navigation apparatus utilizes a so-called GPS (Global Positioning System) as well as another system for independently obtaining the traveling direction and distance of the vehicle from a predetermined reference point (more specifically, the starting point from which the vehicle travels), so as to detect the current position of the vehicle.
Many of the conventional navigation apparatus are provided with a gyro-sensor and an accelerometer for detecting acceleration applied to the vehicle, in order to obtain the current position, traveling direction and/or change in velocity of the vehicle with the use of the above-mentioned system for independently obtaining the current position thereof.
The conventional sensor such as the gyro-sensor and accelerometer has a detection reference axis along which the direction and amount of acceleration are detected. In actual cases, such a detection reference axis is provided in the form of a physical element or an imaginary element, taking into consideration the direction of acceleration to be detected by means of the sensor. The positional determination of such a detection reference axis relative to the sensor is made without taking into consideration a possibility that the navigation apparatus in which the sensor is mounted, may not be disposed on a horizontal plane. More specifically, these sensors having the predetermined characteristic features are mounted on the navigation apparatus, on the assumption that the respective detection reference axes are in parallel with a ground on which the vehicle drives. In such a case, the navigation apparatus is disposed on the vehicle so as to be also in parallel with the ground.
On the other hand, miniaturization of the navigation apparatus has recently advanced, thus making it possible to dispose the navigation apparatus in a central console of the vehicle.
With respect to an operation for disposing the navigation apparatus in the central console, in many cases, the navigation apparatus is placed so that the front surface of an operation panel of the navigation apparatus, on which a display unit and operation switches such as buttons are placed, is inclined relative to the vertical direction so as to face upward, in view of improvement in viewability of the display unit and operability of the switches. In a case where the navigation apparatus is placed on or under the other audio apparatus in the central console, the navigation apparatus is usually disposed so that the front surface of the operation panel is inclined relative to the vertical direction so as to face upward. Such a positional relationship can be achieved by mounting the navigation apparatus in itself in the central console in a tilted state (more specifically, so that the rear side of the navigation apparatus (which is the front side in the traveling direction of the vehicle) is placed lower than the front side thereof.
The switches such as the buttons of the navigation apparatus are usually operated with lower frequency than those of the other audio apparatus. Such a tendency may lead to a situation that the navigation apparatus is placed under the other audio apparatus in the central console. As a result, there may be a case where the inclination angle of the navigation apparatus as mounted relative to the horizontal plane becomes excessively large (more specifically, over the allowable angle (for example, 30 degrees) as described later.
In the above-described case, the direction of the detection reference axis of the sensor greatly deviates from the direction of acceleration actually applied to the sensor during an actual detection (i.e., the horizontal direction), thus causing an error such as offset in sensitivity of the sensor. As a result, there occur problems of deterioration of accuracy of positioning the current position and velocity of the vehicle.
Now, such problems will be described more in detail with reference to FIG. 8. FIG. 8 is a descriptive view illustrating the central console 102 in which the navigation apparatus 100 provided with the accelerometer 101 is mounted.
When the navigation apparatus 100 is inclined relative to the horizontal plane so that the operation panel 103 faces upward so as to be fitted into a receiving space of the central console 102, as shown in FIG. 8, the detection reference axis xe2x80x9cGxe2x80x9d of the accelerometer 101 is also inclined relative to the horizontal plane by the mounting angle xe2x80x9c"THgr"xe2x80x9d of the navigation apparatus 100 in accordance with the inclination thereof.
If the assumption is made that the vehicle drives forward to move rightward in FIG. 8, the acceleration actually applied to the navigation apparatus 100 during such a forward movement can be expressed by xe2x80x9cAxxe2x80x9d having the opposite directional component to the forward movement.
When the acceleration xe2x80x9cAxxe2x80x9d actually applied to the navigation apparatus 100 is detected by means of the accelerometer 101 having the detection reference axis, which is inclined by the mounting angle xe2x80x9c"THgr"xe2x80x9d of the navigation apparatus 100, the accelerometer 101 outputs the acceleration xe2x80x9cGx (Gx=cos"THgr"xc3x97Ax)xe2x80x9d as the detection result, which has the smaller value than the actually applied acceleration xe2x80x9cAxxe2x80x9d.
On the other hand, acceleration vertically and upwardly applied to the navigation apparatus 100 (i.e., the vertically and upwardly applied thereto due to vibration of the vehicle and an impactive force from the ground) can be expressed by the acceleration xe2x80x9cAzxe2x80x9d, which is perpendicular to the above-mentioned acceleration xe2x80x9cAxxe2x80x9d.
When the acceleration xe2x80x9cAzxe2x80x9d actually applied to the navigation apparatus 100 is detected by means of the accelerometer 101 in the same manner as the acceleration xe2x80x9cAzxe2x80x9d, the accelerometer 101 outputs the acceleration xe2x80x9cGz (Gz=sin"THgr"xc3x97Az)xe2x80x9d as the detection result, which is the sine element of the actually applied acceleration xe2x80x9cAzxe2x80x9d.
The acceleration xe2x80x9cAtxe2x80x9d, which is detected through vector sum of the accelerations xe2x80x9cGxxe2x80x9d and xe2x80x9cGzxe2x80x9d as mentioned above by the accelerometer 101, can be expressed by the following formula:
At=Gx+Gz=cos"THgr"xc3x97Ax+sin"THgr"xc3x97Az
The resultant acceleration xe2x80x9cAtxe2x80x9d differs from the acceleration xe2x80x9cAxxe2x80x9d to be actually detected. Such a difference causes an error, which deteriorates accuracy of positioning the current position of the vehicle. As the mounting angle xe2x80x9c"THgr"xe2x80x9d of the navigation apparatus 100 increases, a tendency that the acceleration xe2x80x9cAxxe2x80x9d to be actually detected is more remarkably influenced by the vertical acceleration xe2x80x9cAzxe2x80x9d, rather than the acceleration xe2x80x9cAxxe2x80x9d in the traveling direction of the vehicle, becomes more remarkable, thus leading to a noticeable error.
The conventional navigation apparatus has recently made a correction of the detection results obtained by the accelerometer or the gyro-sensor through a processing operation based on software for correcting the error. In addition, there has also been adopted a system for improving the accuracy of correction through a continuous learning process along with the movement of the vehicle.
However, the error correction carried out by the above-mentioned processing operation does not provide sufficient correcting effects, immediately after the navigation apparatus is mounted on the vehicle, thus causing a problem.
In addition, even when the error correction is carried out utilizing the software for correcting the error, an increased mounting angle xe2x80x9c"THgr"xe2x80x9d (for example, exceeding 30 degrees) may be outside the range of allowable angle, which has been predetermined for the sensor, thus also causing a problem.
It is conceivable to dispose the sensor in the navigation apparatus in the manufacturing process so that the above-mentioned mounting angle is decreased, thus avoiding the error of positioning due to the above-mentioned mounting angle. In such a case, it is necessary to dispose the sensor in the navigation apparatus so as to be inclined in a predetermined direction through specific measures or structural components, for the purpose of avoiding the above-mentioned error. Consequently, this leads to increased cost for manufacturing the navigation apparatus and reduction in yields.
In addition, disposing the sensor in the navigation apparatus so as to be inclined may hinder an effective use of the limited space in the casing of the navigation apparatus. Giving a higher priority to the above-mentioned measures to avoid the error may have an influence on the size of the navigation apparatus.
An object of the present invention, which was made to solve the above-mentioned problems, is therefore to provide a sensing apparatus, which detects acceleration applied to a vehicle, without causing an error of positioning due to the above-mentioned mounting angle, thus avoiding the problems of increased cost for manufacturing the navigation apparatus and reduction in yields, on the one hand, and an electronic equipment to be mounted on a movable body, which utilizes such a sensing apparatus.
In order to attain the aforementioned object, the sensing apparatus of the first aspect of the present invention comprises:
a sensing unit for detecting a direction and an amount of physical quantity applied thereto, said sensing unit having a detection reference axis along which the direction and the amount of the physical quantity are detected; and
a supporting unit for stationarily supporting said sensing unit;
wherein:
said sensing unit is inclined relative to said supporting unit by an angle, said angle being predetermined so that a difference in angle between said detection reference axis and the direction of said physical quantity actually applied to said sensing unit when detecting the direction and the amount of said physical quantity is minimized.
Here, the sensing unit is inclined clockwise or counterclockwise relative to the direction of the physical quantity on a plane including the direction of the physical quantity.
Securing the sensing unit on the supporting unit so that the above-mentioned difference in angle is minimized makes it possible to accurately detect the amount and direction of the physical quantity.
In a case where the detected results from the sensing apparatus is subjected to an optional correction operation such as a processing operation to provide more accurate results, the range of possible error to be corrected is remarkably expanded, since the above-mentioned difference in angle is minimized in the sensing apparatus in itself.
In addition, it is possible to amount the sensing apparatus on an electronic equipment in the same manner as the conventional measures or through the conventional fitting elements during the manufacture of such an electronic equipment, without taking into consideration any measures to reduce the above-mentioned difference in angle. As a result, an effective use of the limited space in the casing of the electronic equipment can be ensured, the manufacturing cost can be decreased and the yields can be improved.
In the second aspect of the present invention, there may be adopted a structure in which said supporting unit comprises a base member and a mounting member secured to said base member; and said sensing unit is mounted on said mounting member.
The above-mentioned difference in angle is minimized by connection of the mounting member, which is placed between the sensing unit and the base member, with the sensing unit, thus making it possible to accurately detect the physical quantity in a simple structure. In addition, with respect to the other structural components than the above, there can be used the corresponding same components in the conventional sensing apparatus, thus making it possible to decrease the manufacturing cost and improve the yields.
In the third aspect of the present invention, there may be adopted a structure in which said mounting member has a slit formed therein; said sensing unit has a counter-slit formed therein; and said sensing unit is mounted on said mounting member so that said counter-slit of said sensing unit engages with said slit of said mounting member.
Merely forming the slit in the mounting member so as to incline to the predetermined direction, by which the above-mentioned difference in angle can be minimized, makes it possible to support the sensing unit on the mounting member in an appropriate manner, thus reducing the manufacturing cost of the sensing apparatus.
The structure in which the counter-slit of the sensing unit engages with the slit of the mounting member ensures an appropriate mounting state of the sensing unit on the mounting member, thus making it possible to manufacture the sensing apparatus in simple manufacturing processes.
In the fourth aspect of the present invention, there may be adopted a structure in which said sensing unit comprises a plurality of detection discs disposed in parallel with each other and a supporting shaft passing through a center of each of said detection discs to support said detection discs thereon, said supporting shaft serving as said detection reference axis; and said supporting shaft is secured to said supporting unit.
The sensing unit includes the supporting shaft, which is inclined so that the above-mentioned difference in angle is minimized. It is therefore possible to accurately detect physical quantity in a simple structure, even when the sensing unit further includes the detection discs supported on the supporting shaft, thus permitting reduction in the manufacturing cost and improvement in yields.
In the fifth aspect of the present invention, there may be adopted a structure in which said detection discs comprises a stationary electrode, which is stationarily supported on said supporting shaft and a pair of movable electrodes, which are supported on said supporting shaft on opposite sides of said stationary electrode so as to be movable in a direction of said supporting shaft.
Such a structure provides an accurate detection of physical quantity in a simple manner, thus permitting reduction in the manufacturing cost and improvement in yields.
Further, in order to attain the aforementioned object, the electronic equipment of the sixth aspect of the present invention comprises:
a main body; and
a sensing apparatus provided in said main body, said sensing apparatus comprising (i) a sensing unit for detecting a direction and an amount of physical quantity applied thereto, said sensing unit having a detection reference axis along which the direction and the amount of the physical quantity are detected; and (ii) a supporting unit for stationarily supporting said sensing unit;
wherein:
said sensing unit is inclined relative to said supporting unit by an angle, said angle being predetermined so that a difference in angle between said detection reference axis and the direction of said physical quantity actually applied to said sensing unit when detecting the direction and the amount of said physical quantity is minimized.
The sensing unit is inclined so that the above-mentioned difference in angle is minimized, taking into consideration a mounting angle, by which the electronic equipment including the sensing unit is mounted on the movable body, thus enabling the sensing unit in the electronic equipment to detect accurately the direction and amount of physical quantity. In addition, the sensing apparatus per se has a structure in which the above-mentioned difference in angle is minimized, without need to provide independently any mechanism for inclining the sensing apparatus in itself. The above-mentioned structure has no influence on the effective use of the limited space in the electronic equipment, which is mountable on the movable body, thus permitting reduction in the manufacturing cost of the electronic equipment and improvement in yields.
The seventh to tenth aspects of the present invention have the same features as those of the above-mentioned second to fifth aspects of the present invention.